1. Field of the Invention
This invention relates to a fuel supply for an engine, and more particularly to a fuel injection system that is suitable for an outboard motor engine.
2. Description of Related Art
In the interest of improving engine performance and particularly fuel efficiency and exhaust emission control, many types of engines now employ a fuel injection system for supplying fuel to the engine. In this system, fuel usually is injected into an air induction device by a fuel injector. This fuel injection has the advantages of permitting the amount of fuel delivered for each cycle of the engine to be precisely adjusted. In addition, by utilizing the fuel injection system, it is possible to maintain the desired fuel air ratio under a wide variety of engine running condition.
An amount of the fuel injected by the fuel injector is usually controlled by a control device in response to the engine running conditions. The fuel is delivered to the fuel injector by a fuel pump under a certain fixed pressure and the duration for injection per unit time, i.e., a duty ratio, is controlled by the control device so that any required amount can be metered. Strict control of the fuel amount is quite important for stable operations of the engine.
Some engines for outboard motors employ such a fuel injection system. The fuel injection system generally includes, other than the fuel injector, a main fuel tank disposed on a hull of the associated watercraft for storing fuel and a fuel reservoir attached on the engine for temporarily storing the fuel. The fuel in the main fuel tank is supplied to the fuel reservoir through a fuel supply conduit and the fuel in the fuel reservoir, in turn, is delivered to the fuel injector through another fuel supply conduit. The excess fuel that has not been injected by the fuel injector is returned to the fuel reservoir through a return conduit.
The engine is, due to being employed for outboard motors, operated quite often in a high speed and high load. The engine, thus, produces much heat under this running condition. In addition, the engine is generally enclosed in a protective cowling assembly and the heat accumulates within the cowling. The circumambient air around the engine, as a matter of course, is heated. The fuel supply conduits, at least in part, and the fuel return conduit extend within the protective cowling assembly and are situated, therefore, under the rigorous circumstances.
Under the circumstances, bubbles or vapor can appear in the fuel and can interfere and degrade the strict control of the fuel amount injected during each duty cycle. Vapor lock may even occur in the fuel supply and/or fuel return conduits. If this happens, the fuel is no longer be supplied or returned to the fuel injector or fuel reservoir and the engine consequently stalls.
In order to inhibit the vapor from appearing in the fuel, the fuel reservoir is usually constructed to also function as a vapor separator. The vapor separator can greatly reduce the chances of the vapor appearing in the fuel. However, the fuel is still situated in the warmed or heated surrounding, a vapor lock can occur and/or the duty ratio can be adversely affected.
One resolution to this problem is disclosed in U.S. Pat. No. 5,309,885. The vapor separator disclosed in this patent has a cooling water jacket disposed next to the reservoir portion. However, this construction invites a large scaled structure of the vapor separator and thus does not work well in outboard motor applications because the outboard motor is only allowed to have a very narrow space around the engine within the protective cowling in which to arrange the vapor separator or fuel reservoir. The kind of construction disclosed in the ""885 patent, thus, cannot be disposed in the space unless the capacity for containing the fuel is reduced.
The problem described above is not limited to outboard motor engines. Other engines which also are employed within tight fitting enclosures suffer the same problem.
A need therefore exists for an improved fuel supply system that can inhibit vapor from appearing in the fuel supplied to a combustion chamber and that also can be placed within a narrow space so as not to increase significantly the girth of the engine.
In accordance with one aspect of the present invention, a fuel injection system is provided for an internal combustion engine. The engine has a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder body and defines a combustion chamber with the cylinder head and the piston. The fuel injection system comprises a fuel injector supplying fuel to the combustion chamber. A fuel reservoir at least temporarily stores the fuel therein. A fuel conduit communicates with at least one of the fuel reservoir and the fuel injector, and a fuel cooling device to cool the fuel passing through the fuel conduit. In this manner, fuel vapor formation is inhibited in the fuel delivered to the fuel injector.
In one mode, the engine includes a first fuel supply conduit that supplies the fuel to the fuel reservoir, and a second fuel supply conduit that supplies the fuel from the fuel reservoir to the fuel injector. A fuel return conduit returns the excess fuel from the fuel injector to the fuel reservoir. The fuel cooling device is provided for cooling the fuel passing through at least one of the first fuel supply conduit, the second fuel supply conduit and the fuel return conduit.
In accordance with another aspect of the present invention, a fuel cooling device is provided for a fuel supply system. The fuel supply system supplies fuel to a combustion chamber of an internal combustion engine through a fuel delivery passage. The fuel cooling device comprises a fuel coolant passage extending, at least in part, along the fuel delivery passage.
In accordance with a further aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder and defines a combustion chamber with the cylinder head and the piston. A fuel injector sprays fuel toward the combustion chamber. Delivering means is provided for delivering the fuel to the fuel injector. The delivering means includes a fuel passage. A cooling mechanism is arranged to cool the fuel passing through the fuel passage.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.